Method and apparatus for vibration casting of vehicle wheels

ABSTRACT

A vehicle wheel mold is vibrated during a casting process. The vibration reduces the solidification time needed to form a wheel casting while improving tensile strength of the wheel.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/092,684, filed on Jul. 13, 1998 and InternationalPatent Application No. PCT/US99/15719, filed on Jul. 12, 1999.

BACKGROUND OF THE INVENTION

[0002] This invention relates in general to casting of vehicle wheelsand in particular to a method and apparatus for vibration casting ofvehicle wheels.

[0003] Vehicle wheels include a circular wheel disc attached to anannular wheel rim. The wheel disc includes a central wheel hub having apilot hole and plurality of wheel mounting holes formed therethrough. Aplurality of equally circumferentially spaced radially extending spokessupport the wheel hub within the wheel rim. The wheel rim is adapted tosupport a pneumatic tire.

[0004] In the past, vehicle wheels typically have been formed entirelyfrom steel. However, one piece wheels formed entirely from light weightmetals, such as aluminum, magnesium and titanium or alloys thereof, arebecoming increasingly popular. In addition to weighing less thanconventional all-steel wheels, such light weight wheels can bemanufactured having a pleasing esthetic shape. Weight savings also canbe achieved with two piece wheels formed by attaching a light weightmetal alloy wheel disc to a steel wheel rim.

[0005] Light weight wheels are typically formed by forging or castingoperations. During a forging operation, a heated billet of the lightweight metal alloy is squeezed by very high pressure between successivesets of dies until the final shape of the wheel is formed. During acasting operation, molten metal is poured or forced under pressure intoa cavity formed in a multi-piece wheel mold. After the metal coolssufficiently to solidify, the mold is opened and a rough wheel castingis removed. The wheel casting is then machined to a final shape.Machining can include turning the outside and inside surfaces of thewheel rim, facing the inboard and outboard wheel disc surfaces anddrilling the center pilot hole and the mounting holes through the wheelhub.

[0006] Conventional casting operations include numerous processes, suchas die casting, low pressure injection casting and gravity casting.Conventional casting operations typically utilize a wheel mold formedfrom a number of movable segments which are opened to allow removable ofthe wheel casting from the mold. Referring now to the drawings, there isillustrated in FIG. 1, generally at 10, a typical multi-segment wheelmold used for gravity casting. The mold 10 includes a base segment 11which supports a plurality of movable side segments 12, two of which areshown in FIG. 1. The side segments 12 can be retracted and extended in ahorizontal direction by a conventional mechanism 13. A movable top core14 extends between the side segments 12. The top core 14 can be raisedand lowered in a vertical direction by the mechanism 13. When the mold10 is closed, the top core 14 cooperates with the side and base segments12 and 11 to define a wheel mold cavity 15. The outline of a finishedvehicle wheel cast in the mold 10 is illustrated in FIG. 1 by the dashedline labeled 16.

[0007] For high volume production of castings, such as vehicle wheels, ahighly automated gravity casting process is frequently used. Suchautomated gravity casting processes typically use a casting machinehaving a plurality of multi-segment molds mounted upon a movingstructure, such as a rotatable carousel. Each mold is indexed past arefractory furnace containing a pool of molten metal. A charge of moltenmetal is poured into a gate formed in the mold which communicates withthe mold cavity. Gravity causes the metal to flow from the gate into themold cavity. The mold and the molten metal cool as the casting machineindexes the other molds to the refractory furnace for charging withmolten metal. After a sufficient cooling time has elapsed for the moltenmetal to solidify, the mold is opened and the wheel casting removed. Themold is then closed and again indexed to the refractory furnace to berefilled with another charge of molten metal.

SUMMARY OF THE INVENTION

[0008] This invention relates to a method and apparatus for vibrationcasting of vehicle wheels. As explained above, casting of vehicle wheelsis a highly automated process. However, the production of a castingmachine is constrained by the length of time required for the moltenmetal to solidify within the individual wheel molds. A reduction in thelength of time needed for the molten metal to solidify would allow anincrease in the speed of operation of the casting machine, therebyincreasing the number of wheels produced in a given time period.Accordingly, it would be desirable to reduce the length of time neededfor the molten metal to solidify.

[0009] The present invention contemplates an apparatus for casting avehicle wheel component which includes a multi-segment mold for thevehicle wheel component and a device for vibrating a portion of themold. In the preferred embodiment, the device for vibrating includes apneumatically powered ball vibrator. The ball vibrator is mountedadjacent to the mold and is operable to vibrate a top core of the mold.The wheel component can be either a one piece vehicle wheel or a fullface wheel disc.

[0010] Alternately, the device for vibrating can be a pneumaticallypowered reciprocating hammer.

[0011] The invention also contemplates a method for forming a vehiclewheel component which includes providing a multi-segment mold forcasting the wheel component and a device for vibrating a portion of thewheel mold. The cavity of the wheel component mold is filled with acharge of molten metal. A portion of the wheel component mold isvibrated while the molten metal solidifies. The wheel component castingis then removed from the mold. The molten metal can be poured into themold cavity with gravity causing the molten metal to flow throughout themold cavity or forced under pressure into the mold cavity with thepressure causing the molten metal to flow throughout the mold cavity.

[0012] Various objects and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the preferred embodiment, when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a sectional view of a multi-segment vehicle wheel moldaccording to the prior art.

[0014]FIG. 2 is a sectional view of a multi-segment vehicle wheel moldin accordance with the invention.

[0015]FIG. 3 is a sectional view of a multi-segment vehicle wheel moldequipped with an alternate embodiment of the invention.

[0016]FIG. 4 is a flow chart for a method for casting a vehicle wheel inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The inventor has determined that vibrating a wheel mold cansignificantly reduce the amount of time needed for the molten metalcontained within the mold cavity to solidify. Referring again to thedrawings, there is illustrated in FIG. 2 a multi-segment wheel mold 20used for gravity casting of wheels which is in accordance with thepresent invention. Components of the mold 20 which are similar tocomponents shown in FIG. 1 have the same numerical designators. As shownin FIG. 2, a conventional commercially available ball vibrator 21 ismounted upon the mold top core 14. The vibrator 21 is secured to the topcore 14 by a plurality of threaded fasteners 22. In the preferredembodiment, the vibrator 21 selected has a base which fits upon the topcore 14 to minimize installation effort and time.

[0018] In the preferred embodiment, the vibrator 21 is operated bycompressed air supplied though an air line 23; however, the inventionalso can be practiced with ball vibrators operated by other mediums,such as a hydraulically powered vibrator, or the vibrator can be poweredby an electric motor. For the vibrator 21 shown, compressed air forces achrome steel ball around bearing grade races to impart vibratory energythrough the top core 14 to the molten metal contained in the mold cavity15.

[0019] The compressed air, which is not affected by the hightemperatures encountered in a foundry, can be supplied from a readilyavailable source, such as tapping into the foundry air supply. Thecompressed air flows though a regulator (not shown) for controlling thepressure to adjust the speed and force of the vibrator. In the preferredembodiment, the air pressure is adjustable over range of from 60 poundsper square inch (psi) to 100 psi.

[0020] The compressed air also flows through either a manual valve or asolenoid valve (not shown) which is connected between the regulator andthe vibrator 21. The valve controls the operation of the vibrator 21. Inthe preferred embodiment, a solenoid valve is utilized with the valvecoil connected to a microprocessor which controls the casting machine.This assures that the vibrator 21 is actuated during the appropriateperiods in the cycle. A filter (not shown) also is included in the airsupply to remove an contaminants from the supplied air which may damagethe vibrator 21. The compressed air is vented from the vibrator 21through an exhaust port 24. An optional muffler (not shown) can beattached to the exhaust port 24 to reduce the noise generated by thedischarge of the compressed air.

[0021] The inventor has found that vibration of the mold 20 while themolten metal contained therein solidifies has significantly reduced thesolidification time for a wheel casting. During tests, thesolidification time has been reduced from six minutes without vibrationto 4 to 5 minutes. Thus, vibration can reduce solidification time by 20to 33 percent. Additionally, the inventor has observed that, withvibration, the microstructure grain size of a wheel casting is reducedfrom the size resulting without vibration. Also, the spacing of thedendrite arms within the casting is reduced when the mold is vibratedwhile the metal solidifies. Accordingly, the tensile strength of thewheel is improved by the application of vibration.

[0022] An alternate embodiment of the invention is illustrated by themold 30 shown in FIG. 3. As before, components of the mold 30 which aresimilar to components shown in FIG. 1 have the same numericaldesignators. As shown in FIG. 3, a conventional pneumatic knock outhammer 31 is mounted adjacent to the mold top core 14. The hammer 31 isheld in position by a mounting bracket (not shown) which is attached tothe mold support mechanism 13. The hammer is 31 actuated by compressedair supplied through an air line 32. Similar to the ball vibrator 21described above, the compressed air is vented through an exhaust port(not shown). The hammer 31 has a reciprocating head 33 which is locatedadjacent to a top plate 34 of the mold top core 14. When actuated, thehammer head 33 taps the top plate 34 to impart vibrations through thetop core 14 to the molten metal contained within the mold cavity 15.Operation of the hammer 31 produces results similar to those describedabove for the ball vibrator 21.

[0023] While the preferred embodiments of the invention have beenillustrated and described above for a ball vibrator 21 and a knock outhammer 31, it will be appreciated that the invention also can bepracticed with other conventional devices for imparting vibrations tothe wheel mold 10. Furthermore, while gravity casting has been shown anddescribed above, it will be appreciated that the invention also can bepracticed with other conventional casting processes, such as, forexample, low pressure and die casting.

[0024] The present invention also contemplates a method for vibratorycasting of a vehicle wheel. The method is illustrated by the flow chartshown in FIG. 4. In functional block 40, a wheel mold, which is equippedwith a vibratory device, is charged with molten metal. The metal may bepoured under gravity or injected into the mold cavity by a low pressure.The vibratory device is activated in functional block 41. The mold isthen vibrated in functional block 42 for a predetermined time period,T₁, which is a function of the volume of metal being cast. In thepreferred embodiment, the vibration time is between 200 and 250 seconds;however, it will be appreciated that the invention also can be practicedwith other vibration time periods. At the end of T₁, the vibratorydevice is turned off, as shown in block 43. The mold and casting areallowed to continue to cool for a additional time period, T₂, infunctional block 44; however, this step is optional. In functional block45, the mold is opened and the wheel casting removed therefrom.

[0025] Additionally, the method can be practiced with vibration beingapplied to the mold while the mold cavity is being charged with themolten metal (not shown). Similarly, the method can include a delaybefore actuating the vibrator to allow the mold to be charged withmolten metal and for the molten metal to be begin to solidify. In thepreferred embodiment, the delay is in the range of from zero to 30seconds; however, it will be appreciated that the invention also can bepracticed with delays which exceed 30 seconds.

[0026] While the preferred embodiment of the invention has beenillustrated and described with vibration applied to the top core of awheel mold, it will be appreciated that the invention also can bepracticed with the vibration applied to other portions of the mold, suchas, for example, to a side segment (not shown). Additionally, vibrationcan be applied simultaneously to a plurality of mold segments (notshown).

[0027] In accordance with the provisions of the patent statutes, theprinciple and mode of operation of this invention have been explainedand illustrated in its preferred embodiment. However, it must beunderstood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope. For example, while the preferred embodiment of the inventionhas been illustrated and described for casting a one piece wheel, itwill be appreciated that the invention also can be practiced for castinga component of a vehicle wheel, such as a full face wheel disc or awheel rim.

What is claimed is:
 1. An apparatus for casting a vehicle wheelcomponent comprising: a multi-segment mold for the vehicle wheelcomponent; and a device for vibrating a portion of said mold while saidmold contains a charge of molten metal and continuing to vibrate saidportion of said mold while said charge of molten metal solidifies.
 2. Anapparatus according to claim 1 wherein said device for vibratingincludes a ball vibrator.
 3. An apparatus according to claim 2 whereinsaid mold includes a top core and further wherein said ball vibrator ismounted adjacent to said mold and is operable to vibrate said top core.4. An apparatus according to claim 3 wherein said ball vibrator ispneumatically powered.
 5. An apparatus according to claim 4 wherein saidmold forms a one piece vehicle wheel.
 6. An apparatus according to claim4 wherein said mold forms a full face wheel disc.
 7. An apparatusaccording to claim 1 wherein said device for vibrating includes areciprocating hammer.
 8. An apparatus according to claim 7 wherein saidmold includes a top core and further wherein said reciprocating hammeris mounted adjacent to said mold and is operable to vibrate said topcore.
 9. An apparatus according to claim 8 wherein said reciprocatinghammer is pneumatically powered.
 10. A method for forming a vehiclewheel component comprising the steps of: (a) providing a multi-segmentmold for casting the wheel component and a device for vibrating aportion of the wheel mold; (b) filling the cavity of the wheel componentmold with a charge of molten metal; (c) vibrating a portion of the wheelcomponent mold while the molten metal solidifies; and (d) removing thewheel component from the mold.
 11. The method according to claim 10wherein during step (c) the portion of the mold is vibrated while themold cavity is filled with the molten metal.
 12. The method according toclaim 10 wherein the portion of the mold is vibrated in step (c) afterthe mold cavity is completely filled.
 13. The method according to claim10 wherein the portion of the mold is vibrated in step (c) after apredetermined time period has elapsed following the filling of the moldcavity.
 14. The method according to claim 10 wherein during step (b) themolten metal is poured into the mold cavity with gravity causing themolten metal to flow throughout the mold cavity.
 15. The methodaccording to claim 10 wherein during step (b) the molten metal is forcedunder pressure into the mold cavity with the pressure causing the moltenmetal to flow throughout the mold cavity.
 16. The method according toclaim 14 wherein the mold forms a one piece vehicle wheel.
 17. Themethod according to claim 14 wherein the mold forms a full face wheeldisc.